Angiogenesis is the formation of new blood vessels by sprouting from pre-existing ones. (Weinstate-Saslow, The FASEB Journal 8: 402-407, 1994; Folkman et al., Science 235: 442-447, 1987). The generation of new blood vessels involves a multistep process, which includes the migration of vascular endothelial cells into tissue, followed by the condensation of such endothelial cells into vessels. Angiogenesis may be induced by an angiogenic agent or be the result of a natural condition. The process is essential to a variety of normal body activities, such as embryo implantation; embryogenesis and development; and wound healing. The process involves a complex interplay of molecules that stimulate and molecules that inhibit the growth and migration of endothelial cells, the primary cells of the capillary blood vessels. (Folkman and Shing, J. Biol. Chem., 267 (16): 10931-34, 1989; Folkman and Klagsbrun, Science, 235, 442-47, 1987).
Several angiogenic agents have been identified. (Hanahan and Folkman, Cell, 86 (3): 353-364, 1996). For example, a number of growth factors have been identified which promote/activate endothelial cells to undergo angiogenesis. These include, by example and not by way of limitation; vascular endothelial growth factor (VEGF); transforming growth factor (TGFβ); acidic and basic fibroblast growth factor (aFGF and bFGF): and platelet derived growth factor (PDGF) (Ferrara and Davis-Smyth, Endocr Rev. 18 (1): 4-25, 1997). VEGF is believed to be a central mediator of angiogenesis. Antibodies directed against VEGF have been shown to suppress tumor growth in vivo and decrease the density of blood vessels in experimental tumors (Kim et al., Nature 362: 841-844, 1993), indicating that VEGF antagonists could have therapeutic applications as inhibitors of tumor-induced angiogenesis.
Normal angiogenic activity is low in healthy adults and limited to certain organs such as the uterus during pregnancy or intensely exercising skeletal muscle. However, its activity increases during injury and in diseases such as cancer, retinopathy, or arthritis, where it contributes to pathological changes. Therefore, angiogenesis can have both the beneficial effects such as facilitating wound healing, and detrimental effects by causing inflammatory diseases such as, for example, rheumatoid arthritis, macular degeneration, psoriasis, and diabetic retinopathy.
Furthermore, it has been shown that angiogenesis is essential for the growth of solid tumors and for tumor metastasis (Bouck et al., Adv Cancer Res.; 69: 135-74, 1996; Yancopoulos et al., Nature 407 (6801): 242-8, 2000). Tumor-induced angiogenesis is initiated by growth factors and cytokines that are released from the tumor or from inflammatory cell infiltrates (Brown et al., Am. J. Path. 143: 1255, 1993; Brown et al., Human Path. 26: 86, 1995; Leek et al., J. Leukocyte Biol. 56: 423, 1994; Hatva et al., Am. J. Pathol. 146: 368, 1995; and Plate et al., Nature 359: 845, 1992). Growth factors and cytokines which are expressed by tumor cells stimulate angiogenesis in a number of animal models including the chick chorioallantoic membrane model, the corneal pocket angiogenesis model, and models involving spontaneous and xenotransplanted tumor growth (Brooks et al., Cell 79: 1157, 1994; Brooks et al., Science 264: 569, 1994; Brooks et al., J. Clin. Invest. 96: 1815, 1995; and Friedlander et al., Science 27: 1500, 1995). Accordingly, tumor-associated angiogenesis is a potential target for therapies that inhibit tumor proliferation, invasion, and metastasis since angiogenesis has been implicated not only in the growth of tumors but also in their metastasis (Liotta et al., 1991, Cell 64: 327; Weinstat-Saslow et al., FASEB J 8: 401, 1994; Blood et al., Biochim. Biophys. Acta 1032: 89, 1990; Folkman, Semin. Cancer Biol. 3: 65, 1992; and Weidner et al., N. Engl. J. Med. 324: 1, 1991).
It has been well recognized that angiogenesis is involved in a variety of diseases or disorders and that such diseases or conditions can be treated by administration of angiogenesis inhibitors. Examples of pathological conditions involving angiogenesis include, but are not limited to, macular degeneration, ocular neovascular glaucoma, diabetic retinopathy, corneal graft rejection, vitamin A deficiency, Sjorgen's disease, acne rosacea, mycobacterium infections, bacterial and fungal ulcers, Herpes simplex infections, systemic lupus, rheumatoid arthritis, osteoarthritis, psoriasis, chronic inflammatory diseases (e.g., ulcerative colitis, Crohn's disease), hereditary diseases such as Osler-Weber Rendu disease and haemorrhagic teleangiectasia.
In an attempt to treat these diseases or conditions, many angiogenesis inhibitors have been discovered. Examples include endostatin (O'Reilly et al., 1997, Cell 88: 277), angiostatin (O'Reilly et al., 1994, Cell 79: 315), peptide CNGRCVSGCAGRC (SEQ ID NO: 3) (Arap et al., 1998, Science 279: 377), cyclic peptide RGDfV (Friedlander et al., 1995, Science 270: 1500), and monoclonal antibodies LM609 and P1F6 (Friedlander et al., 1995, Science 270: 1500). These drugs appear to target only on the angiogenesis aspect of the diseases without treating other additional, underlying mechanisms that are associated with or involved in the pathogenesis of the aforementioned diseases.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies, especially in connection with the method of identifying drug candidates for treating cancer, inflammatory diseases, and/or angiogenesis-associated diseases.